BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a filtering medium for selective adsorption of blood
components, and a blood filter.
2. Description of the Related Art
[0002] In the field of blood transfusion, whole blood preparations, erythrocyte preparations,
platelet preparations, plasma preparations, and the like are used depending on the
use of a blood recipient. In recent years, a so-called leukocyte removal blood transfusion,
in which leukocytes contained in such blood preparations are removed, and then the
blood preparations are transfused, has become widespread.
[0003] For example,
JP3172542B discloses a "filter material for trapping leukocytes, which is characterized in that
a porous body filter material of a three-dimensional network continuous structure,
which is formed from at least one polymer material, and which has an average pore
diameter of 1 to 60 µm, a specific surface area of 0.5 to 10 m
2/g, a porosity of 30% to 95%, a bubble point of 0.08 to 0.30 kg/cm
2, a wall thickness of 0.1 to 9.0 mm, and a surface porosity of 6% to 90%, was fixed
to at least one surface of a fiber filter material made of nonwoven fabric" ([Claim
1]).
[0004] In addition,
WO2005/120600A discloses "a filter for removing leukocytes characterized by containing a porous
filter material in which an osmotic coefficient (kx) in a direction in which the filter
is perpendicular to a filtration surface is 0.5 × 10
-12 m
2 or more and 2.0 × 10
-12 m
2 or less, and a ratio (ky/kx) of an osmotic coefficient (ky) in a direction in which
the filter is parallel to a filtration surface, to kx is 0.5 or more and 1.5 or less,
in the filter for removing leukocytes from a leukocyte-containing liquid, in which
a container having a liquid inlet and an outlet is filled with the porous filter material"
([Claim 4]); discloses a filter material formed from a fiber aggregate such as a nonwoven
fabric, or from a porous body as the porous filter material; and discloses a material
such as cellulose acetate as a material of the porous body (<0030>).
SUMMARY OF THE INVENTION
[0005] The inventors of the present invention have conducted examinations on the known materials
of the related art, which are disclosed in
JP3172542B,
WO2005/120600A, and the like as a filtering medium which selectively adsorbs blood components such
as a leukocyte, and have elucidated that, depending on the type of a polymer material
to be used, a removal (trapping) rate of leukocytes may be remarkably decreased in
some cases according to conditions of sterilization treatment applied to the filtering
medium.
[0006] Accordingly, an object of the present invention is to provide a filtering medium
for selective adsorption of blood components, which is excellent in selective removal
of blood components such as a leukocyte; and a blood filter formed of the filtering
medium.
[0007] As a result of intensive studies to achieve the above object, the inventors of the
present invention have found that a filtering medium containing cellulose acylate,
and having a glass transition temperature of 126°C or higher, and an average through-hole
diameter and a specific surface area within a predetermined range, is excellent in
selective removal of blood components such as a leukocyte, and therefore have completed
the present invention.
[0008] That is, the inventors have found that the above-described object can be achieved
by the following configuration.
- [1] A filtering medium for selective adsorption of blood components, which contains
a cellulose acylate, and has a glass transition temperature of 126°C or higher, an
average through-hole diameter of 0.1 to 50 µm, and a specific surface area of 1.0
to 100 m2/g.
- [2] The filtering medium for selective adsorption of blood components according to
[1], in which a substitution degree of an acyl group included in the cellulose acylate
is within a range of 1.00 to 2.90.
- [3] The filtering medium for selective adsorption of blood components according to
[1] or [2], in which the acyl group included in the cellulose acylate has 4 or less
carbon atoms.
- [4] The filtering medium for selective adsorption of blood components according to
any one of [1] to [3], in which the acyl group included in the cellulose acylate includes
at least an acetyl group.
- [5] The filtering medium for selective adsorption of blood components according to
any one of [1] to [4], in which the cellulose acylate constitutes at least a part
of a surface of a member that comes into contact with blood.
- [6] The filtering medium for selective adsorption of blood components according to
any one of [1] to [5], which is a nonwoven fabric or a porous membrane.
- [7] The filtering medium for selective adsorption of blood components according to
any one of [1] to [5], which is a nonwoven fabric made of fibers having an average
fiber diameter of 1 nm to 5 µm and an average fiber length of 1 mm to 1 m.
- [8] The filtering medium for selective adsorption of blood components according to
any one of [1] to [7], which selectively adsorbs a blood cell component among the
blood components.
- [9] The filtering medium for selective adsorption of blood components according to
any one of [1] to [8], which selectively adsorbs a leukocyte component among the blood
components.
- [10] A blood filter which is filled with the filtering medium for selective adsorption
of blood components according to any one of [1] to [9].
[0009] According to the present invention, it is possible to provide a filtering medium
for selective adsorption of blood components, which is excellent in selective removal
of blood components such as a leukocyte; and a blood filter formed of the filtering
medium.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] Hereinafter, the invention will be described in detail.
[0011] The explanation of the configuration requirements described below is based on representative
embodiments of the invention; however, the invention is not intended to be limited
to such embodiments.
[0012] According to the present specification, a numerical value range indicated using "to"
means a range including the numerical values described before and after "to" as the
lower limit and the upper limit.
[Filtering medium for selective adsorption of blood components]
[0013] A filtering medium for selective adsorption of blood components of the embodiment
of the present invention (hereinafter abbreviated simply as the "filtering medium
for adsorption of the embodiment of the present invention") contains a cellulose acylate.
[0014] In addition, the filtering medium for adsorption of the embodiment of the present
invention has a glass transition temperature of 126°C or higher, an average through-hole
diameter of 0.1 to 50 µm, and a specific surface area of 1.0 to 100 m
2/g.
[0015] Here, the "cellulose acylate" refers to a cellulose ester in which some or all of
the hydrogen atoms that constitute hydroxyl groups of cellulose, that is, free hydroxyl
groups existing at the 2-position, 3-position, and 6-position of a β-1,4-bonded glucose
unit, have been substituted with acyl groups.
[0016] As described above, because the filtering medium for adsorption of the embodiment
of the present invention contains a cellulose acylate, and has the glass transition
temperature of 126°C or higher, the average through-hole diameter of 0.1 to 50 µm,
and the specific surface area of 1.0 to 100 m
2/g, the filtering medium is excellent in selective removal of blood components such
as a leukocyte.
[0017] The reason why such effects are exhibited is not clearly known in detail; however,
the inventors of the present invention speculate the reason as follows.
[0018] In other words, in the present invention, it is considered that a degree of freedom
in designing an average through-hole diameter and a specific surface area increases
since a cellulose acylate can also be adsorbed onto blood components (particularly
a leukocyte) directly or through a protein; or a glass transition temperature of the
filtering medium is high since a cellulose acylate is contained, and therefore defects
such as clogging can be suppressed even in a case where the filtering medium is exposed
to a high temperature state by sterilization treatment or the like.
[0019] In the present invention, the glass transition temperature of the filtering medium
for selective adsorption of blood components is 126°C or higher, but is preferably
135°C or higher, more preferably 145°C or higher, and even more preferably 150°C to
300°C, from the reason of improving a selective removal rate of blood components (particularly
a leukocyte).
[0020] The "glass transition temperature" can be obtained as a temperature at an intersection
of a straight line obtained by extending a base line on a low temperature side to
a high temperature side, and a tangential line drawn at an inflection point of a curve
of a stepwise changing portion of glass transition, in a curve derived from the glass
transition of a cellulose acylate obtained in a case of measurement at a rate of temperature
increase of 10°C/min using a Differential Scanning Calorimeter (DSC). The measurement
is carried out in two cycles, and a temperature obtained from a curve of a second
cycle by the above-mentioned method is referred to as a glass transition temperature.
In this case, in a first cycle, at a rate of temperature increase of 10°C/min, the
filtering medium is heated to a temperature at least 30°C higher than that at the
time of the completion of the glass transition in a case of a non-crystalline state,
and the filtering medium is heated to a temperature at least 30°C higher than that
at the time of the completion of a melting peak in a case of a crystalline state.
The filtering medium is kept at each temperature for 10 minutes, and then rapidly
cooled to a temperature about 50°C below the glass transition temperature. In addition,
the second cycle is performed following the first cycle, and a curve obtained by heating
at a rate of temperature increase of 10°C/min is used for calculation of a glass transition
point.
[0021] Furthermore, the "glass transition temperature" can be appropriately adjusted depending
on a substitution degree of cellulose acylate contained in the filtering medium for
adsorption of the embodiment of the present invention, the type of substituents, and
the like.
[0022] The filtering medium for selective adsorption of blood components of the embodiment
of the present invention has not only an effect of removing blood components by adsorption
but also a separation and removal effect due to a size difference between different
blood cell components. According to these two effects, different kinds of blood components
can be effectively separated. In the present invention, an optimal size as an average
through-hole diameter of the filtering medium can be appropriately selected for a
blood component to be separated, but for selective separation, the average through-hole
diameter of the filtering medium for selective adsorption of blood components is 0.1
to 50 µm, and is preferably 4.5 to 30 µm and more preferably 5 to 15 µm from the reason
of improving a selective removal rate of blood components (particularly a leukocyte).
[0023] Herein, the "average through-hole diameter" is evaluated by increasing air pressure
to 2 cc/min with respect to a sample completely wetted by GALWICK (manufactured by
Porous Materials, Inc.) in a pore size distribution measurement test using a perm
porometer (CFE-1200 AEX manufactured by Seika Corporation), in the same manner as
in the method described in paragraph <0093> of
JP2012-046843A. Specifically, with respect to a membrane sample completely wetted by GALWICK, a
certain amount of air was fed at 2 cc/min to one side of the membrane, and while measuring
a pressure thereof, a flow rate of air permeating to an opposite side of the membrane
is measured. In this method, firstly, data on pressure and permeated air flow rate
(hereinafter referred to as a "wet curve") is obtained for the membrane sample wetted
by GALWICK. Next, the same data (hereinafter referred to as a "dry curve") was measured
for the membrane sample in a dry state, and a pressure at an intersection of a curve
(half dry curve) corresponding to half of a dry curve flow rate and the wet curve
is calculated. Thereafter, an average through-hole diameter can be calculated by introducing
a surface tension (γ) of GALWICK, a contact angle (θ) with the filtering medium, and
an air pressure (P) into Formula (I).
[0024] In addition, a method for adjusting the "average through-hole diameter" is not particularly
limited. For example, in a case where a form of the filtering medium for adsorption
of the embodiment of the present invention is a nonwoven fabric made of nanofibers,
in a case where a plurality of nozzles are used upon spinning using a nanofiber manufacturing
apparatus, a part of the nozzles is used as a nozzle for supplying a polyvinyl alcohol
aqueous solution, and a hole diameter can be adjusted by adjusting the number of these
nozzles. That is, after the nonwoven fabric made of cellulose acylate and polyvinyl
alcohol is produced, the hole diameter can be adjusted by immersing the nonwoven fabric
in water to dissolve the polyvinyl alcohol.
[0025] In the present invention, a specific surface area of the filtering medium for selective
adsorption of blood components is 1.0 to 100 m
2/g, but is preferably 1 to 50 m
2/g and more preferably 3 to 50 m
2/g from the reason of further improving the selective removal rate of blood components
(particularly a leukocyte).
[0026] Herein, the "specific surface area" refers to a measurement value measured by Brunauer-Emmett-Teller
(BET) method by nitrogen adsorption.
[0027] In addition, the "specific surface area" can be appropriately adjusted by, for example,
a fiber diameter of a fiber made of cellulose acylate, impartment of unevenness to
a fiber surface, and the like.
[0028] In the present invention, a thickness of the filtering medium for selective adsorption
of blood components is not particularly limited, but may be 5 µm to 30,000 µm, preferably
10 µm to 3,000 µm, and more preferably 10 µm to 500 µm from the viewpoint of imparting
a sufficient space volume and a sufficient mechanical strength which are for allowing
the filtering medium to hold a subject to be removed, from the viewpoint of compatibility
between a low filtration pressure and a high separation capacity, and the like.
[0029] The thickness can be obtained by measuring a membrane thickness of the filtering
medium at 10 points using a micrometer (manufactured by Mitutoyo) and averaging the
respective measured values.
[Cellulose acylate]
[0030] In the present invention, a substitution degree with an acyl group included in the
cellulose acylate is preferably within a range of 1.00 to 2.90, more preferably within
a range of 2.00 to 2.90, and even more preferably within a range of 2.80 to 2.90 from
the reason of further improving a selective removal rate of blood components (particularly
a leukocyte).
[0031] Herein, the "substitution degree" refers to a substitution degree of the hydrogen
atoms that constitute hydroxyl groups of cellulose with acyl groups (hereinafter will
also be referred to as "acylation degree"), and the substitution degree can be calculated
by comparing the area intensity ratio of carbons of cellulose acylate measured by
a
13C-NMR method.
[0032] In addition, the "substitution degree" of the acyl group can be appropriately adjusted
by a method in which a partial hydrolysis time is changed when synthesizing the cellulose
acylate, a method in which alkaline saponification is performed after producing a
nonwoven fabric or a porous membrane, and the like.
[0033] Specific examples of the acyl group include an acetyl group, a propionyl group, a
butyryl group, and the like.
[0034] The acyl groups to be substituted may be composed only of a single kind (for example,
only an acetyl group) or may be of two or more kinds.
[0035] In the present invention, from the reason of improving uniformity of a fiber diameter
and improving the appearance in a case where a nonwoven fabric is produced, the number
of carbon atoms of the acyl group included in the cellulose acylate is preferably
4 or less, and a acetyl group is preferable.
[0036] The cellulose acylate in which the acyl group is the acetyl group will also be referred
to as "cellulose acetate" in the following explanation.
[0037] A number average molecular weight (Mn) of the cellulose acylate is not particularly
limited, but is preferably 40,000 or more, more preferably 40,000 to 150,000, and
even more preferably 60,000 to 100,000 from the viewpoint of strength.
[0038] In addition, a weight-average molecular weight (Mw) of the cellulose acylate is not
particularly limited, but is preferably 100,000 or more, more preferably 100,000 to
500,000, and even more preferably 150,000 to 300,000 from the viewpoint of the mechanical
strength of the fiber composite.
[0039] The weight-average molecular weight or number average molecular weight according
to the present specification is a value measured by a gel permeation chromatography
(GPC) method under the following conditions.
- Apparatus name: HLC-8220 GPC (Tosoh Corporation)
- Type of column: TSK gel Super HZ4000 and HZ2000 (Tosoh Corporation)
- Eluent: Dimethylformamide (DMF)
- Flow rate: 1 ml/min
- Detector: RI
- Sample concentration: 0.5%
- Calibration curve base resin: TSK standard polystyrene (molecular weights 1,050, 5,970,
18,100, 37,900, 190,000, and 706,000)
<Method for synthesizing cellulose acylate>
(Raw material)
[0041] Regarding a raw material of cellulose, suitable examples include raw materials originating
from hardwood pulp, softwood pulp, cotton linter, and the like. Among them, raw materials
originating from cotton linter are preferred because an amount of hemicellulose is
small, and a nanofiber having further improved uniformity of the fiber diameter can
be produced.
(Activation)
[0042] It is preferable that the raw material of cellulose is subjected to a treatment of
contacting with an activating agent (activation), prior to acylation.
[0043] Specific examples of the activating agent include acetate, propionic acid, butyric
acid, and the like, and among them, acetate is preferred.
[0044] The amount of addition of the activating agent is preferably 5% to 10,000%, more
preferably 10% to 2,000%, and even more preferably 30% to 1,000%.
[0045] The method for addition can be selected from methods such as spraying, dropwise addition,
and immersion.
[0046] Activation time is preferably 20 minutes to 72 hours, and more preferably 20 minutes
to 12 hours.
[0047] The activation temperature is preferably 0°C to 90°C, and more preferably 20°C to
60°C.
[0048] Furthermore, an acylation catalyst such as sulfuric acid may be added to the activating
agent, in an amount of 0.1% to 10% by mass.
(Acylation)
[0049] It is preferable for synthesizing a uniform cellulose acylate that the hydroxyl groups
of cellulose are acylated by reacting cellulose with an acid anhydride of a carboxylic
acid using Brønsted acid or a Lewis acid (see "
Rikagaku Shoten (Dictionary of Physics and Chemistry," 5th Edition (2000)) as a catalyst, and control of the molecular weight is also enabled.
[0050] Examples of the method for obtaining a cellulose acylate include a method of causing
a reaction by adding two kinds of carboxylic acid anhydrides as acylating agents as
a mixture or in sequence to the system; a method of using a mixed acid anhydride of
two kinds of carboxylic acids (for example, a mixed acid anhydride of acetate and
propionic acid); a method of forming a mixed acid anhydride (for example, an acid
anhydride of acetate and propionic acid) within the reaction system by using acid
anhydrides of a carboxylic acid and another carboxylic acid (for example, acid anhydrides
of acetate and propionic acid) as raw materials, and reacting the mixed acid anhydride
with cellulose; and a method of first synthesizing a cellulose acylate having a substitution
degree of less than 3, and further acylating residual hydroxyl groups by using an
acid anhydride or an acid halide.
<Acid anhydride>
[0052] The acid anhydride of a carboxylic acid is preferably an acid anhydride of a carboxylic
acid having 2 to 6 carbon atoms, and specifically, suitable examples include acetic
anhydride, propionic anhydride, butyric anhydride, and the like.
[0053] It is preferable that the acid anhydride is added in an amount of 1.1 to 50 equivalents,
more preferably 1.2 to 30 equivalents, and even more preferably 1.5 to 10 equivalents,
with respect to the hydroxyl groups of cellulose.
<Catalyst>
[0054] Regarding the acylation catalyst, it is preferable to use a Brønsted acid or a Lewis
acid, and it is more preferable to use sulfuric acid or perchloric acid.
[0055] The amount of addition of the acylation catalyst is preferably 0.1% to 30% by mass,
more preferably 1% to 15% by mass, and even more preferably 3% to 12% by mass.
<Solvent>
[0056] Regarding the acylation solvent, it is preferable to use a carboxylic acid, and it
is more preferable to use a carboxylic acid having from 2 to 7 carbon atoms. Specifically,
it is even more preferable to use, for example, acetate, propionic acid, butyric acid,
or the like. These solvents may also be used as mixtures.
<Condition>
[0057] In order to control a temperature increase caused by the heat of reaction of acylation,
it is preferable that the acylating agent is cooled in advance.
[0058] An acylation temperature is preferably -50°C to 50°C, more preferably -30°C to 40°C,
and even more preferably -20°C to 35°C.
[0059] A minimum temperature of the reaction is preferably -50°C or higher, more preferably
-30°C or higher, and even more preferably -20°C or higher.
[0060] An acylation time is preferably 0.5 hours to 24 hours, more preferably 1 hour to
12 hours, and even more preferably 1.5 hours to 10 hours.
[0061] Adjustment of the molecular weight is enabled by controlling the acylation time.
<Reaction terminating agent>
[0062] It is preferable that a reaction terminating agent is added after the acylation reaction.
[0063] The reaction terminating agent may be any compound capable of decomposing an acid
anhydride, and specific examples thereof include water, an alcohol having 1 to 3 carbon
atoms, and a carboxylic acid (for example, acetate, propionic acid, butyric acid,
or the like). Above all, a mixture of water and a carboxylic acid (acetate) is preferred.
[0064] A composition of water and the carboxylic acid is such that a content of water is
preferably 5% to 80% by mass, more preferably 10% to 60% by mass, and even more preferably
15% to 50% by mass.
<Neutralizing agent>
[0065] After termination of the acylation reaction, a neutralizing agent may be added.
[0066] Examples of the neutralizing agent include ammonium, organic quaternary ammoniums,
alkali metals, metals of Group 2, metals of Groups 3 to 12, and carbonates, hydrogen
carbonates, organic acid salts, hydroxides, or oxides of the elements of Groups 13
to 15. Specifically, suitable examples include carbonate, hydrogen carbonate, acetate,
or hydroxide of sodium, potassium, magnesium, or calcium.
<Partial hydrolysis>
[0067] The cellulose acylate obtained by the acylation described above has a total substitution
degree of almost 3; however, for the purpose of adjusting the substitution degree
to a desired value (for example, degree of about 2.8), the acyl substitution degree
of the cellulose acylate can be decreased to a desired extent, by partially hydrolyzing
ester bonds by maintaining the cellulose acylate for several minutes to several days
at 20°C to 90°C in the presence of water and a small amount of catalyst (for example,
an acylation catalyst such as residual sulfuric acid). Meanwhile, partial hydrolysis
can be terminated as appropriate using residual catalyst and the neutralizing agent.
<Filtration>
[0068] Filtration may be carried out in any process between the completion of acylation
and reprecipitation. It is also preferable to dilute the system with an appropriate
solvent prior to filtration.
<Reprecipitation>
[0069] A cellulose acylate solution can be mixed with water or an aqueous solution of a
carboxylic acid (for example, acetate, propionic acid, or the like), and thus reprecipitation
can be induced. Reprecipitation may be any of continuous type or batch type.
<Washing>
[0070] After reprecipitation, it is preferable to perform a washing treatment. Washing is
carried out using water or warm water, and completion of washing can be checked through
the pH, ion concentration, electrical conductivity, elemental analysis, or the like.
<Stabilization>
[0071] It is preferable that a weak alkali (carbonate, hydrogen carbonate, hydroxide, or
oxide of Na, K, Ca, Mg, or the like) is added to the cellulose acylate obtained after
washing, for the purpose of stabilization.
<Drying>
[0072] It is preferable that the cellulose acylate is dried at 50°C to 160°C until a percentage
moisture content reaches 2% by mass or less.
[0073] In the present invention, it is preferable that the above-mentioned cellulose acylate
constitutes at least a part of the surface of the member that comes into contact with
blood, for the reason of further improving the selective removal rate of blood components
(particularly a leukocyte). It is considered that this is because an adsorption performance
of the cellulose acylate itself to a blood component is easily exhibited.
[0074] Herein, the "surface of the member that comes into contact with blood" refers to
a surface of a portion where the filtering medium for adsorption of the embodiment
of the present invention comes into contact with blood. For example, in a case where
the filtering medium for adsorption of the embodiment of the present invention is
a nonwoven fabric, the surface refers to a surface of a fiber constituting the nonwoven
fabric; and in a case where the filtering medium for adsorption of the embodiment
of the present invention is a porous membrane, the surface refers to a surface of
the porous membrane and a wall surface of an internal cavity.
[0075] The filtering medium for adsorption of the embodiment of the present invention is
preferably in the form of a nonwoven fabric or a porous membrane, and is more preferably
a nonwoven fabric.
[0076] In addition, as a nonwoven fabric, a nonwoven fabric made of fibers having an average
fiber diameter of 1 nm to 5 µm and an average fiber length of 1 mm to 1 m is preferable,
a nonwoven fabric made of nanofibers having an average fiber diameter of 100 nm and
or more and less than 1,000 nm and an average fiber length of 1.5 mm to 1 m is more
preferable, and a nonwoven fabric made of nanofibers having an average fiber diameter
of 100 nm to 800 nm and an average fiber length of 2.0 mm to 1 m is even more preferable.
[0077] The average fiber diameter and average fiber length can be adjusted by adjusting
a concentration of a cellulose acylate solution in a case of producing the nonwoven
fabric.
[0078] The average fiber diameter means a value measured as follows.
[0079] The surface of a nonwoven fabric formed from fibers is observed by taking a Transmission
Electron Microscope (TEM) image or a Scanning Electron Microscope (SEM) image.
[0080] An observation based on an electron microscopic image is performed at a magnification
ratio selected from 1,000 times to 5,000 times depending on the size of the constituent
fiber. However, the sample, the observation conditions, and the magnification ratio
are adjusted so as to satisfy the following conditions.
- (1) One straight line X is drawn at any site within an image to be observed, and 20
or more fibers intersect this straight line X.
- (2) A straight line Y perpendicularly intersecting the straight line X is drawn in
the same image, and 20 or more fibers intersect the straight line Y.
[0081] In regard to the electron microscopic observation images such as described above,
for each of the fibers intersecting the straight line X and the fibers intersecting
the straight line Y, widths (minor axis of the fiber) of at least 20 fibers (that
is, at least 40 fibers in total) are read out. In this manner, an observation of at
least 3 sets or more of the electron microscopic images such as described above is
made, and fiber diameters of at least 40 fibers × 3 sets (that is, at least 120 fibers)
are read out.
[0082] The average fiber diameter is determined by averaging the fiber diameters read out
as such.
[0083] The average fiber length means a value measured as follows.
[0084] That is, the fiber length of the fiber can be determined by analyzing the electron
microscopic observation image used on the occasion of measuring the average fiber
diameter described above.
[0085] Specifically, in the electron microscopic observation image such as described above,
for each of the fibers intersecting the straight line X and the fibers intersecting
the straight line Y, fiber lengths of at least 20 fibers (that is, at least 40 fibers
in total) are read out.
[0086] In this manner, an observation of at least 3 sets or more of the electron microscopic
images such as described above is made, and the fiber lengths of at least 40 fibers
× 3 sets (that is, at least 120 fibers) are read out.
[0087] The average fiber length is determined by averaging the fiber lengths read out as
such.
<Manufacture process of filtering medium>
[0088] In the present invention, a method for producing the nanofiber is not particularly
limited; however, a production method utilizing an electrospinning method (hereinafter
will also be referred to as "electrospinning method") is preferable, and the nanofiber
can be produced by, for example, discharging a solution obtained by dissolving the
above-described cellulose acylate in a solvent, from a distal end of a nozzle at a
constant temperature in the range of from 5°C to 40°C, applying a voltage between
the solution and a collector, and jetting out fibers from the solution into the collector.
Specifically, the nanofiber can be produced by a method shown in paragraphs <0014>
to <0044> and Figs. 1 and 2 of
JP2016-053232A, and the like.
[0089] In addition, a method for producing the nonwoven fabric is not limited, and a nonwoven
fabric 120 can be manufactured by a nanofiber manufacturing apparatus 110 shown in
Fig. 1 of
JP2016-053232A, for example.
[0090] Meanwhile, a method for producing a porous membrane is not limited. For example,
using a coating solution containing a cellulose acylate, a good solvent in which the
cellulose acylate dissolves, a solvent in which the cellulose acylate does not dissolve
but the cellulose acylate dissolves, and a poor solvent which easily causes phase
separation, the poor solvent is phase-separated at the same time when the dissolved
cellulose acylate precipitates at the time of drying after coating, the poor solvent
is evaporated to be removed, and therefore a porous membrane having holes formed therein
can be formed.
<Fiber adhesion treatment process of filtering medium>
[0091] In a process of manufacturing the filtering medium for selective adsorption of blood
components of the embodiment of the present invention, in order to make fibers adhere
to each other, a heat fusion welding process or an adhesion treatment process may
be included during a process of manufacturing the nonwoven fabric or after a process
of manufacturing the nonwoven fabric by using a nanofiber manufacturing apparatus.
[0092] The filtering medium for adsorption of the embodiment of the present invention is
preferably used as a filtering medium which selectively adsorbs a blood cell component,
and is more preferably used as a filtering medium which selectively adsorbs a leukocyte
component, among blood components.
[Blood filter]
[0093] A blood filter of the embodiment of the present invention is a blood filter filled
with the above-described filtering medium for selective adsorption of blood components
of the embodiment of the present invention.
[0094] Examples of such a blood filter include, in a case where the filtering medium for
selective adsorption of blood components is in the form of a nonwoven fabric, a module
in which a nonwoven fabric is set in a housing in a flat membrane shape, a spiral-type
module in which a filtering medium formed into a cylindrical nonwoven fabric is set
in a housing.
Examples
[0095] Hereinafter, the present invention will be described in more detail based on Examples.
The materials, amounts used, proportions, treatments, treatment procedures, and the
like disclosed in the following Examples can be modified as appropriate as long as
the gist of the invention is maintained. Therefore, the scope of the invention should
not be limitedly interpreted by the Examples described below.
[Examples 1 to 3]
<Synthesis of cellulose acetate>
[0096] Cellulose (raw material: cotton linter) was mixed with acetate and sulfuric acid,
and the mixture was acetylated while a reaction temperature was maintained at 40°C
or lower.
[0097] After the raw material cellulose disappeared and acetylation was completed, the system
was further heated continuously at a temperature of 40°C or lower, and the degree
of polymerization was adjusted to a desired value.
[0098] Next, residual acid anhydride was hydrolyzed by adding an aqueous solution of acetate,
and then partial hydrolysis was performed by heating at a temperature of 60°C or lower.
Thus, the substitution degree was adjusted as shown in Table 1.
[0099] Residual sulfuric acid was neutralized with an excess amount of magnesium acetate.
Reprecipitation from the aqueous solution of acetate was performed, and washing with
water was repeated. Thus, a cellulose acetate was synthesized.
<Production of nonwoven fabric>
[0100] The cellulose acetate thus synthesized was dissolved in a mixed solvent of 88% of
dichloromethane and 12% of methanol to prepare a cellulose acetate solution having
a concentration of 3.5 g/100 cm
3. Therefore, a nonwoven fabric having a size of 20 × 30 cm and formed from cellulose
acetate nanofibers was produced using a nanofiber manufacturing apparatus having a
plurality of nozzles, and used as a filtering medium for selective adsorption of blood
components.
[Example 4 and Comparative Example 1]
[0101] A nonwoven fabric formed from cellulose acetate nanofibers was produced in the same
manner as in Example 1 to be used as a filtering medium for selective adsorption of
blood components, except that, in a part of nozzles in a nanofiber manufacturing apparatus,
spinning is performed using a polyvinyl alcohol (PVA) aqueous solution instead of
the cellulose acetate solution, and the part of nozzles is immersed in water after
spinning to remove PVA in the case of producing a nonwoven fabric.
[Examples 5 and 6 and Comparative Example 2]
[0102] A nonwoven fabric formed from cellulose acetate nanofibers was produced in the same
manner as in Example 1 to be used as a filtering medium for selective adsorption of
blood components, except that a substitution degree was adjusted as shown in Table
1.
[Example 7]
[0103] A nonwoven fabric formed from cellulose propionate nanofibers was produced in the
same manner as in Example 1 to be used as a filtering medium for selective adsorption
of blood components, except that an acyl group was changed from an acetyl group to
a propionyl group, and a substitution degree was adjusted as shown in Table 1.
[Example 8]
[0104] A nonwoven fabric formed from cellulose butanoate nanofibers was produced in the
same manner as in Example 1 to be used as a filtering medium for selective adsorption
of blood components, except that an acyl group was changed from an acetyl group to
a butyryl group, and a substitution degree was adjusted as shown in Table 1.
[Comparative Example 3]
[0105] A nonwoven fabric formed from carboxymethylcellulose nanofibers was produced in the
same manner as in Example 1 to be used as a filtering medium for selective adsorption
of blood components, except that carboxymethylcellulose having a substitution degree
shown in Table 1 was used instead of cellulose acetate.
[Comparative Example 4]
[0106] A nonwoven fabric formed from ethyl cellulose nanofibers was produced in the same
manner as in Example 1 to be used as a filtering medium for selective adsorption of
blood components, except that ethyl cellulose having a substitution degree shown in
Table 1 was used instead of cellulose acetate, and methyl ethyl ketone was used instead
of a mixed solvent.
[Examples 9 to 11]
[0107] A nonwoven fabric formed from cellulose acetate nanofibers was produced in the same
manner as in Example 1 to be used as a filtering medium for selective adsorption of
blood components, except that a substitution degree was adjusted as shown in Table
1.
[Comparative Example 5]
[0108] After producing the nanofiber nonwoven fabric in the same manner as in Example 1,
the nanofiber nonwoven fabric was immersed in an aqueous solution of 0.5 N sodium
hydroxide to which 5% ethanol was added, for 48 hours.
[0109] After immersion, the nanofiber nonwoven fabric was immersed in pure water, then washed
and dried, and therefore a nonwoven fabric made from deacylated cellulose was produced
and used as a filtering medium for selective adsorption of blood components. Because
a substitution degree of cellulose acetate deacylated under the same conditions is
0.00, a substitution degree in Comparative Example 5 in Table 1 is denoted as "0.00"
because of non-substitution.
[Example 12]
<Preparation of dope>
[0110] A dope having a composition shown below was prepared.
[0111] Specifically, cellulose acetate was dissolved in dimethyl chloride, and methanol
was added to this solution little by little. Next, glycerin and pure water were added
little by little to this solution to prepare a solution in a state of having almost
no undissolved matter. The solution was filtered through a filter paper, and therefore
a dope was prepared.
(Dope composition)
• Cellulose acetate (acetylation degree: 60.8%) |
5 parts by mass |
• Glycerin |
0.2 parts by mass |
• Dimethylchloride |
55 parts by mass |
• Methanol |
34 parts by mass |
• Pure water |
6 parts by mass |
<Production of porous membrane>
[0112] The prepared dope was sent by a gear pump, further filtrated, and then cast from
a die onto a polyethylene terephthalate (PET) film which was carried on an endless
band and conveyed.
[0113] This cast membrane was dried for 20 minutes with drying air at 20°C to 40°C.
[0114] From the endless band, the film was peeled off with PET. The peeled off film was
dried for 15 minutes at 80°C to 120°C with hot air and wound with a winder. In the
cellulose acetate on PET, a large number of fine pores were formed.
[0115] Using a peeling bar, the cellulose acetate microporous membrane was separated from
PET and used as a filtering medium for selective adsorption of blood components.
[Comparative Example 6]
[0116] A nonwoven fabric formed from cellulose acetate nanofibers was produced in the same
manner as in Example 1 to be used as a filtering medium for selective adsorption of
blood components, except that, in a part of nozzles in a nanofiber manufacturing apparatus,
spinning is performed using a polyvinyl alcohol (PVA) aqueous solution instead of
the cellulose acetate solution, and the part of nozzles is immersed in water after
spinning to remove PVA in the case of producing a nonwoven fabric.
[Comparative Example 7]
[0117] A filtering medium for selective adsorption of blood components was obtained in the
same manner as in Example 1 except that a thickness of the nonwoven fabric was increased
5 times and the produced nonwoven fabric was subjected to a compress process at a
pressure of 1 MPa in a membrane thickness direction.
[Comparative Example 8]
[0118] Polyacrylonitrile was dissolved in N,N-dimethylformamide (DMF) to prepare 3.5 g/100
cm
3 polyacrylonitrile. Therefore, a nonwoven fabric having a size of 20 × 30 cm and formed
from polyacrylonitrile nanofibers was produced using a nanofiber manufacturing apparatus
having a plurality of nozzles, and used as a filtering medium for selective adsorption
of blood components.
[Comparative Example 9]
[0119] A nonwoven fabric formed from polyacrylonitril nanofibers was produced in the same
manner as in Example 8 to be used as a filtering medium for selective adsorption of
blood components, except that, in a part of nozzles in a nanofiber manufacturing apparatus,
spinning is performed using a polyvinyl alcohol (PVA) aqueous solution instead of
the cellulose acetate solution, and the part of nozzles is immersed in water after
spinning to remove PVA in the case of producing a nonwoven fabric.
[Comparative Example 10]
[0120] Dissolution was performed in NMP so that polyurethane became 14% by mass, methylcellulose
became 14% by mass, and calcium chloride dihydrate became 1.4% by mass.
[0121] Next, this solution was coated on a PET film and immersed in a 50% by mass NMP aqueous
solution at 50°C to coagulate.
[0122] Next, the film was washed with pure water and dried in an oven at 55°C to produce
a polyurethane porous membrane, which was used as a filtering medium for selective
adsorption of blood components.
[Comparative Example 11]
[0123] Polypropylene was dissolved in a mixed solvent having a mass ratio of decalin, acetone,
and DMF of 8:1:1 so as to become 12.5% by mass. Therefore, a nonwoven fabric having
a size of 20 × 30 cm and formed from polypropylene was produced using a nanofiber
manufacturing apparatus having a plurality of nozzles, and used as a filtering medium
for selective adsorption of blood components.
[Comparative Example 12]
[0124] With reference to a method disclosed in
JP1993-087808A (
JP-H05-087808A), cellulose acetate pellets were injection molded to form beads of 3.2 mmϕ, followed
by five extraction operations at 50°C for 1 hour in methanol. The pellets were air-dried
for 15 hours and further dried at 80°C for 5 hours to obtain a filtering medium for
selective adsorption of blood components.
[Example 13]
[0125] Cellulose acetate propionate (CAP-482-20 manufactured by Eastman Chemical Company)
was dissolved in a mixed solvent of 88% dichloromethane and 12% methanol to prepare
a cellulose acetate propionate solution of 7.5 g/100 cm
3. Using a nanofiber manufacturing apparatus having a plurality of nozzles, a nonwoven
fabric made of cellulose acetate propionate fibers of 20 × 30 cm was produced.
[0126] Next, the prepared nonwoven fabric was treated at 200°C for 5 minutes using a constant
temperature drier, and then taken out to produce a filtering medium for selective
adsorption of blood components.
[Example 14]
[0127] Cellulose acetate butyrate (CAB-381-20 manufactured by Eastman Chemical Company)
was dissolved in a mixed solvent of 88% dichloromethane and 12% methanol to prepare
a cellulose acetate butyrate solution of 7.5 g/100 cm
3. Using a nanofiber manufacturing apparatus having a plurality of nozzles, a nonwoven
fabric made of cellulose acetate butyrate fibers of 20 × 30 cm was produced.
[0128] Next, the prepared nonwoven fabric was treated at 180°C for 5 minutes using a constant
temperature drier, and then taken out to produce a filtering medium for selective
adsorption of blood components.
[Example 15]
[0129] A nonwoven fabric formed of cellulose acetate fiber and cellulose acetate propionate
fiber was produced a solution to be supplied to a part of the nozzles in the nanofiber
manufacturing apparatus of Example 13 was used instead of the cellulose acetate propionate
solution, and the cellulose acetate of Example 1 was dissolved in a mixed solvent
of 88% dichloromethane and 12% methanol to obtain a solution of 5.8 g/100 cm
3 to be subjected to spinning. The number ratio of the nozzles supplied with each solution
was set to 2:1 of cellulose acetate solution:cellulose acetate propionate solution.
[0130] Next, the prepared nonwoven fabric was treated at 230°C for 5 minutes using a constant
temperature drier, and then taken out to produce a filtering medium for selective
adsorption of blood components.
[0131] A material of the produced filtering medium for selective adsorption of blood components,
a thickness of the filtering medium, a substitution degree, a form, an average fiber
diameter, an average fiber length, a glass transition temperature, an average through-hole
diameter, and a specific surface area are shown in Table 1. A substitution degrees
of CAP and CAB described in Examples 13 to 15 are shown in Table 2.
[0132] In Table 1, materials shown in alphabetical notation are the materials as shown below.
CA: cellulose acetate
CP: Cellulose propionate
CB: cellulose butyrate
CMC: Carboxymethylcellulose
EC: Ethyl cellulose
PU: Polyurethane
PAN: Polyacrylonitrile
PP: Polypropylene
CAP: Cellulose acetate propionate
CAB: Cellulose acetate butyrate
[Evaluation]
[0133] Before carrying out evaluations described below, high-pressure steam sterilization
treatment was performed on the produced filtering medium for selective adsorption
of blood components under conditions of 134°C for 30 minutes, using a high pressure
steam sterilizer.
<Removal rate of leukocytes>
[0134] A syringe was set up so that a flange portion faces upward, and the filtering medium
was set at the bottom part.
[0135] Next, 1.5 ml of human whole blood was added dropwise, filtered under a constant pressure,
collected from a lower part of the syringe. The number of leukocytes before and after
passing through the filtering medium was obtained by blood analysis, and a removal
rate of leukocytes was calculated from the following equation. The results are shown
in Table 1.
<Clogging>
[0136] A syringe was set up so that a flange portion faces upward, and the filtering medium
was set at the bottom part.
[0137] Next, 1.5 ml of human whole blood was added dropwise, a constant pressure was applied,
and filtered. 20 ml of the blood was further filtered.
[0138] Next, a filtration rate in a case where 1.5 ml was filtered again was measured and
compared with the initial 1.5 ml filtration rate to carry out evaluation in the following
three stages. The results are shown in Table 1.
1: 1 time or more and less than 1.2 times the initial rate
2: 1.2 times or more and less than 2 times the initial rate
3: 2 or more times the initial rate
[Table 1]
|
Material |
Substitution degree |
Form |
Thickness |
Average fiber diameter |
Average fiber length |
Glass transition temperature |
Average through-hole diameter |
Specific surface area |
Removal rate of leukocytes |
Clogging |
µm |
nm |
mm |
°C |
µm |
m2/g |
% |
- |
Example 1 |
CA |
2.88 |
Nonwoven fabric |
67 |
516 |
4.5 |
177 |
9.9 |
6.9 |
100 |
1 |
Example 2 |
CA |
2.88 |
Nonwoven fabric |
68 |
520 |
4.5 |
177 |
5.7 |
7.3 |
100 |
1 |
Example 3 |
CA |
2.88 |
Nonwoven fabric |
59 |
515 |
4.4 |
177 |
27.3 |
6.0 |
96 |
1 |
Example 4 |
CA |
2.88 |
Nonwoven fabric |
65 |
503 |
4.4 |
177 |
4.4 |
7.0 |
100 |
2 |
Comparative Example 1 |
CA |
2.88 |
Nonwoven fabric |
60 |
525 |
4.4 |
177 |
51.3 |
5.5 |
86 |
1 |
Example 5 |
CA |
2.43 |
Nonwoven fabric |
86 |
114 |
3.6 |
192 |
10.6 |
44.3 |
100 |
1 |
Example 6 |
CA |
2.43 |
Nonwoven fabric |
72 |
987 |
2.2 |
192 |
10.6 |
1.3 |
96 |
1 |
Comparative Example 2 |
CA |
2.43 |
Nonwoven fabric |
77 |
994 |
2.3 |
192 |
10.8 |
0.9 |
91 |
1 |
Example 7 |
CP |
2.33 |
Nonwoven fabric |
69 |
635 |
3.9 |
154 |
6.6 |
5.6 |
98 |
1 |
Example 8 |
CB |
2.02 |
Nonwoven fabric |
70 |
622 |
4.0 |
138 |
7.8 |
5.7 |
96 |
1 |
Comparative Example 3 |
CMC |
1.41 |
Nonwoven fabric |
66 |
531 |
3.3 |
*1 |
8.0 |
5.8 |
90 |
1 |
Comparative Example 4 |
EC |
1.30 |
Nonwoven fabric |
61 |
627 |
3.8 |
134 |
9.8 |
5.0 |
89 |
1 |
Example 9 |
CA |
2.01 |
Nonwoven fabric |
69 |
488 |
4.3 |
201 |
10.1 |
6.5 |
98 |
1 |
Example 10 |
CA |
1.12 |
Nonwoven fabric |
67 |
479 |
4.2 |
215 |
10.0 |
6.6 |
96 |
1 |
Example 11 |
CA |
0.50 |
Nonwoven fabric |
67 |
473 |
4.2 |
225 |
10.2 |
6.7 |
95 |
1 |
Comparative Example 5 |
Cellulose |
0.00 |
Nonwoven fabric |
68 |
466 |
4.1 |
240 |
10.3 |
6.8 |
88 |
1 |
Example 12 |
CA |
2.88 |
Porous membrane |
231 |
- |
- |
177 |
8.9 |
6.3 |
100 |
1 |
Comparative Example 6 |
CA |
2.88 |
Nonwoven fabric |
58 |
514 |
4.1 |
177 |
108.9 |
5.7 |
36 |
1 |
Comparative Example 7 |
CA |
2.88 |
Nonwoven fabric |
79 |
521 |
4.1 |
177 |
0.09 |
6.1 |
100 |
3 |
Comparative Example 8 |
PAN |
- |
Nonwoven fabric |
33 |
557 |
3.8 |
103 |
5.5 |
5.2 |
100 |
3 |
Comparative Example 9 |
PAN |
- |
Nonwoven fabric |
30 |
567 |
3.8 |
103 |
9.5 |
5.0 |
67 |
2 |
Comparative Example 10 |
PU |
- |
Porous membrane |
289 |
- |
- |
-51 |
7.5 |
1.8 |
*2 |
*2 |
Comparative Example 11 |
PP |
- |
Nonwoven fabric |
367 |
831 |
2.1 |
0 |
3.4 |
3.3 |
100 |
3 |
Comparative Example 12 |
CA |
2.27 |
3.2 mmϕ beads |
- |
- |
- |
195 |
- |
0.05 |
54 |
1 |
Example 13 |
CAP |
*3 |
Nonwoven fabric |
175 |
1529 |
5.8 |
149 |
7.1 |
4.3 |
98 |
1 |
Example 14 |
CAB |
*3 |
Nonwoven fabric |
181 |
1261 |
6.3 |
142 |
8.6 |
5.1 |
98 |
1 |
Example 15 |
CA/CAP |
CA (2.88) /CAP (*3) |
Nonwoven fabric |
222 |
1756 |
5.9 |
177/149*4 |
9.0 |
4.4 |
97 |
1 |
*1: A glass transition temperature could not be checked.
*2: Blood did not permeate the filtering medium, and thus could not be filtered.
*3: Substitution degrees of CAP or CAB described in Table 2 were used.
*4: Each of glass transition temperatures of CA and CAP was checked. |
[Table 2]
|
Substitution degree |
Remarks |
Acetyl group |
Propionyl group |
Butanoyl group |
CAP |
0.15 |
2.63 |
0 |
CAP-482-20 manufactured by Eastman Chemical Company |
CAB |
1.00 |
0 |
1.70 |
CAB-381-20 manufactured by Eastman Chemical Company |
[0139] Based on the results shown in Table 1, it was found that, in a case where a nonwoven
fabric having an average through-hole diameter of more than 50 µm was used as a filtering
medium for selective adsorption of blood components, a removal rate of leukocytes
was poor (Comparative Example 1).
[0140] In addition, it was found that, in a case where a nonwoven fabric having a specific
surface area of less than 1.0 m
2/g was used as a filtering medium for selective adsorption of blood components, a
removal rate of leukocytes was poor (Comparative Example 2).
[0141] Furthermore, it was found that, in a case where a nonwoven fabric containing a cellulosic
material not corresponding to cellulose acylate was used as a filtering medium for
selective adsorption of blood components, a removal rate of leukocytes was poor (Comparative
Examples 3 to 5).
[0142] Furthermore, it was found that, in a case where a nonwoven fabric having an average
through-hole diameter outside the range of 0.1 to 50 µm is used as a filtering medium
for selective adsorption of blood components, a removal rate of leukocytes was poor,
or clogging occurred (Comparative Example 6 and 7).
[0143] Furthermore, it was found that, in a case where a nonwoven fabric containing materials
other than cellulosic materials was used as a filtering medium for selective adsorption
of blood components, a removal rate of leukocytes was poor, or clogging occurred (Comparative
Examples 8 to 11). This is considered to be mainly caused by deformation of the filtering
medium due to the high-pressure steam sterilization treatment.
[0144] Furthermore, it was found that the filtering medium formed of beads having no through-holes
and having a specific surface area of less than 1.0 m
2/g was poor in a removal rate of leukocytes (Comparative Example 12).
[0145] With respect to the above results, it was found that, in a case where a porous membrane
or a nonwoven fabric containing cellulose acylate, and having a glass transition temperature
of 126°C or higher, an average through-hole diameter of 0.1 to 50 µm, and a specific
surface area of 1.0 to 100 m
2/g was used as a filtering medium for selective adsorption of blood components, a
removal rate of leukocytes increased while suppressing clogging (Examples 1 to 15).